Guidelines for monitoring of phytoplankton species composition, abundance and biomass.

Abstract

Phytoplankton primary producers constitute the basis of the pelagic food web and phytoplankton community composition directly affects the nutrition, growth, reproduction and survival of different organisms (see Hällfors & Uusitalo 2013 and references therein) as well as the biogeochemical cycles of the Baltic Sea (Tamelander & Heiskanen 2004, Spilling & Lindström 2008). In addition to providing data on the food web, phytoplankton monitoring provides essential information on the consequences of eutrophication and climate change (Suikkanen et al. 2007, 2013, Hällfors et al. 2013a, Kuosa et al. 2017). In the Baltic Sea, eutrophication has resulted in increases in summer phytoplankton abundance and biomass (Carstensen & Heiskanen 2007, Fleming-Lehtinen et al. 2008, Jaanus et al. 2011) as well as more frequent and intense blooms (Finni et al. 2001, Carstensen et al. 2007, Kahru and Elmgren 2014). Also, the phytoplankton species composition has been observed to change with different nutrient levels and ratios (Gasiunaite et al. 2005, Carstensen & Heiskanen 2007, Suikkanen et al. 2007, Jurgensone et al. 2011). Long-term monitoring has enabled determination of the annual phytoplankton succession and facilitates the recognizing of aberrant phenomena and their progression in the phytoplankton community (e.g. Hajdu et al. 2006, Fleming & Kaitala 2006, Klais et al. 2011, Majaneva et al. 2012, Olli et al. 2013). Phytoplankton monitoring also provides data on the biodiversity of phytoplankton communities (Uusitalo et al. 2013, Hällfors 2013, Olli et al. 2014), on harmful taxa (Leppänen et al. 1995, Wasmund 2002), and makes possible the detection of invasive alien species (Olenina et al. 2010). In addition, phytoplankton indicators derived from the monitoring data can be used for assessing the status of the marine environment (Uusitalo et al. 2013, Lehtinen et al. 2016, Wasmund et al. 2017). Phytoplankton species composition, abundance and biomass are monitored by counting phytoplankton from preserved water samples using the Utermöhl inverted light microscopical method (Utermöhl 1958), by the relevant authorities. 1.2 Purpose and aims In short, analysis of phytoplankton species composition, abundance and biomass is carried out for the following purposes: • to describe temporal trends in phytoplankton species composition, phytoplankton abundance, biomass as well as the intensity and occurrence of blooms • to describe the spatial distribution of phytoplankton species • to identify key phytoplankton species (e.g. dominating, harmful, potential non-indigenous and/or invasive species, as well as indicator species) • to provide basic data for complex ecosystem analyses, food web studies, modelling as well as political and social requirements such as indicators in the frame of the Marine Strategy Framework Directive of the European Union (MSFD; European Union 2008) and the EU Water Framework Directive (WFD; European Union 2000).